docs(ui): move diagnostic export block above findings list

When the findings list grows the diagnostic-export subsection got
pushed below the visible viewport. Moving it above the findings list
(but below the Refresh header and description) keeps the Download
button in reach regardless of how many checks fire.

Wrapped in a subtle gray box to visually distinguish it from the
checks themselves.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pkg/service/handlers/web/index.html

@@ -1555,10 +1555,8 @@
             findings that may need attention. Quick fixes are offered
             for issues the service knows how to remediate.
         </p>
-        <div id="health-generated-at" style="font-size: 0.8em; color: #888; margin-bottom: 10px;"></div>
-        <div id="health-findings">Loading…</div>
 
-        <div style="margin-top: 24px; padding-top: 16px; border-top: 1px solid #eee;">
+        <div style="margin: 12px 0 16px 0; padding: 10px 12px; background: #fafafa; border: 1px solid #eee; border-radius: 4px;">
             <div style="display: flex; align-items: center; gap: 12px; flex-wrap: wrap;">
                 <button onclick="downloadDiagnostic()" title="Download an encrypted diagnostic report to share with the project maintainer">Download diagnostic report</button>
                 <span style="font-size: 0.9em; color: #555;">Share a diagnostic snapshot with the project maintainer.</span>
@@ -1578,6 +1576,9 @@
             </details>
             <div id="health-diagnostic-status" style="font-size: 0.85em; margin-top: 8px;"></div>
         </div>
+
+        <div id="health-generated-at" style="font-size: 0.8em; color: #888; margin-bottom: 10px;"></div>
+        <div id="health-findings">Loading…</div>
     </div>
 
     <!-- Tab 8: Logs -->